A very common laboratory operation is heating a round-bottomed flask or other round-bottomed vessel. Flasks can be heated with a flame from a burner but this is very hazardous when associated with flammable solvents often found in laboratories. Steam baths are safer but require a source of steam and this method is otherwise usually not favored due to complications from liquid water present in steam lines, the need to drain condensate water from the bath and temperature control limitations.
Most commonly today, round-bottomed vessels are heated either with heating mantles or with a fluid-filled baths placed on electrical heat sources such as hotplates. Heating mantles are typically constructed from woven-glass-fiber fabric and from glass wool stuffing enclosing a resistance wire or other heating element. Usually the heating mantle is constructed to form a rounded pocket and sized to closely fit the contours of a flask of a certain capacity such as 100 ml, 500 mL, 1 L, 20 L, etc. Consequently, a different heating mantle is required for each size of flask which will likely be heated in the course of laboratory operations and thus an investment in a number of heating mantles is often required. In addition, typically required is a voltage regulating device such as a variable transformer in order to regulate the heat output of the heating mantle. Adjusting such a device to the proper voltage output to achieve a steady temperature is often a matter of trial-and-error. To automatically maintain a temperature set-point may require an additional, separate piece of equipment. To magnetically stir the contents of the round-bottomed flask requires a rotating-magnet device placed under the heating mantle and a magnetic follower in the vessel. However, even with such an arrangement of rotating-magnet device, heating mantle and magnetic follower, satisfactory stirring can fail as the thickness of the heating mantle will separate the rotating magnet from the magnetic follower to the extent that interaction and synchronization of the two magnets is poor.
A fluid-filled bath set on a hotplate can serve as a medium of heat conduction between a flat heating surface and a round-bottomed vessel placed in the bath. Temperature control is usually simpler than with a heating mantle since hotplates often feature digital temperature controls and a thermocouple probe which may be placed in the fluid-filled bath or in the vessel, itself. The bath may be filled with several types of fluids but silicone oil is preferred since it is non-flammable and can be found in grades which are both high boiling and have high decomposition temperatures. The negative aspects of using an oil bath include the following: spillage, the need to adjust of the bath oil level for the displacement of different sized vessels and the need to adjust fluid levels for optimal magnetic stirring height. Any water contamination of the oil will cause oil spattering when the bath is later heated above the boiling point of water. Spillage can occur due to moving and storage of liquid-filled vessels, tipping of fluid-filled baths on jacks or platforms, overflowing due to the thermal expansion of the liquid, cracking or breaking of glass baths and so forth.
Aluminum blocks are found which are formed with both bowl-shaped cavities to receive rounded vessels and with flat bottoms to sit flat on a hotplate. Like heating mantles these aluminum heating blocks are specifically sized for each size of vessel and thus a considerable cost is incurred in obtaining several heating blocks for several different sizes of vessels. Devices which integrate heating blocks with hotplate-type controllers are also available and are purportedly able to accommodate up to three sizes of round vessels. But their utility is typically limited to rounded vessels, because, lacking a flat heating surface, they typically cannot be used as a typical hotplate is used.
Consequently a device is needed which will sit on a hot plate device and transmit heat to a round-bottomed vessel or other rounded apparatus. Further it is desirable for such a device to allow magnetic stirring of the contents of the vessel by means of a magnetic follower placed in the flask. Further it is desirable that such a device be easily adaptable to round bottomed vessels of various sizes and that it be relatively inexpensive to manufacture and easy to use.